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How to create a Negative for Molds?

Posted: Fri Dec 28, 2018 3:16 am
by jmone
Is it possible to create a Negative in Simplify3D so you can use it as a mold? I'd tried to do a two process setup
1) Target STL with 1 Shell and 0 Infill
2) Box a bit bigger and placed around the Target STL with 100% (or whatever) infill

I was hoping to see in the preview a void in the shape of the Target STL but it was solid (though I could see the 1 Shell in the middle of the fill for the box).

Any other ideas?

Thanks
Nathan

Re: How to create a Negative for Molds?

Posted: Fri Dec 28, 2018 8:00 am
by zemlin
Do that with your modeling software.

Re: How to create a Negative for Molds?

Posted: Sun Dec 30, 2018 3:07 am
by horst.w
Build the negative molde separatly,
how to do, have a look to Youtube >>> "casting pla" , "casting green sands" , "casting silicone" .
A very informative video - german spoken - is here: https://www.youtube.com/watch?v=xn5d9P0TL-c .

Instead PLA you can use filaments from Polymaker "PolyCast Wax-Filaments" (the only-one I know). The difference is, PLA must funnel out and PolyCast becomes vaporized without any remains and debris.


horst.w
GER

Re: How to create a Negative for Molds?

Posted: Sun Dec 30, 2018 2:34 pm
by greybeard
There are several App’s that can manipulate .STL files (if you’re not able-to / familiar-with CAD/other App’s for modeling).

I’ve designed many Molds for injection molding and Homemade molds for Polyurethane, RTV, Silicone and, Hot-Glue. It's fun.

Modeling your gizmo is preferred, of course.
However, if you have a .STL of the gizmo you want to mold, then, you can do this to make a mold:

1) You need:
1 - the gizmo .STL
2 - a Base .STL for the Mold base
You can use most any App to create the base and save as .STL. Most likely, simple are Rectangle/Box...

2) With those Two .STL parts (base and gizmo), find an App that can do Boolean Subtraction’s (Differences).

Adjust the Height & Placement of the parts as needed then,
Subtract (Difference) the Gizmo from the Base to get a pocket of the Gizmo’s shape.
Naturally, if you want a ‘Split’ mold, do it for the Upper and Lower mold sections.

You can make a hole in the top section and pour in the mold material, if not simply using the bottom section and pouring goop into it. Clamp the two sections together. Make an Air Vent hole too for displaced air.

EXAMPLE:

I did this example using FreeCAD for the above approach (modeled it and exported .STL of Base and theThing. Normally, I would simple make the full mold in CAD).
I then loaded the .STL’s and Differenced them to get the mold.

Of course, there are details you’ll consider, such as scaling to compensate for material shrinkage and part-ejection…

Good luck…

Re: How to create a Negative for Molds?

Posted: Sun Dec 30, 2018 3:00 pm
by greybeard
ADDED
Thought I'd add additional info:

I used rubber molding material from Tap Plastic's to make these molds from 3D-Printed parts.

Simple - just pour into a container (I used a frozen food container).
Set your part in the container at desired height (support it with something small).
Pour in the material around your part and - bingo!

Re: How to create a Negative for Molds?

Posted: Mon Dec 31, 2018 5:01 pm
by jmone
Thanks for the advice - FYI, I'm trying a bunch of different methods and started documenting it over on the Prusa Forum.

Re: How to create a Negative for Molds?

Posted: Tue Jan 01, 2019 5:25 am
by horst.w
I have followed your link - (won't enter as member there)

the best low temp metal I have found is "Roses Metal" with only 96°C melting temp.
This has many advantages and the importante one is, that the platic molde stays stabil.

I attache pics of a reparation of a gear, the loosen tooth was replaced by a tooth of Roses Metal.
The form is build with "Plaast Polymorph" ( https://www.bengs-modellbau.de/magazin/ ... unststoff/ ), but later I must print a ABS-Model because the Polymorph becomes soft when the temperature is over 54°C and the Roses metal doesn't cool down as fast as it needed and the tooth is deformed.

H.
IMG_20181217_162615.jpg
IMG_20181217_184711.jpg

Re: How to create a Negative for Molds?

Posted: Tue Jan 01, 2019 11:55 pm
by gearsawe
To use S3D only to make a "mold" of an existing SLT
This requires you have the model you want you want to make a model of plus a box in an ST format.
1. Import the model.
2. add an offset the original offset. for example if the the Z is 6.00. change to 7.00 to have a 1mm offset from build base.
3. take note of Z scale in my example is 12.00
step3.png
4. Import a box.stl scale box to surround the model. for example 20x20x13. 13 because 12 plus the 1 mm offset
step4.png
5. Make sure both model are selected, then In S3D select File>>Export Models>>Export Binary STL. don't save over your orginal file. added something to it like "mold"
6. remove the imported files. then import the Mold Model.
7. process the model! you now have a negative to fill.
step7.png
So it is kind of possible with S3D only

Re: How to create a Negative for Molds?

Posted: Wed Jan 02, 2019 2:14 am
by dkightley
Very clever!! What an ingenious use of S3D's quirks!!

Re: How to create a Negative for Molds?

Posted: Wed Jan 02, 2019 4:19 am
by horst.w
I have no pain to subtract a model from a outer box in my CAD, but your tip is really brilliant - when it would run for me ;)

I have reproduced this step by step but the imported Mold-STL isn't subtracted the model from the box. And this is my experiance in other cases.
What I do wrong or is the list of steps not complete?
What version of S3D are you using?

In former versions were overlapping of models handled as two bodies (each one had its own perimeters) but with one of the previous versions (3.x ?) this principe was given up. Regretfully!

H.